How can I automatically mark pool addresses down when one ISP fails with GTM acting as Link Controller with multiple ISP's?

This is the solution provided by F5 support. I have configured it and it is running but I haven't actually "tested" it yet. The only shortcoming from my original ideal is that both the GTM and LTM are doing upstream monitoring through the gateways, but I'm thinking that might not be a bad thing if one of them fails and the other is still working.

As we discussed, I have opened Service Request 1-347018108 to track your request to monitor an ISP Link; to ensure that the LTM and GTM mark the appropriate configuration items as unavailable at the time of an ISP failure.

On the GTM, apply the following Solution:

SOL6848: Monitoring link objects on  BI-IP GTM or BI-IP Link Controller system
http://support.f5.com/kb/en-us/solutions/public/6000/800/sol6848.html

For the LTM:

SOL7215: Configuring multiple default routes on the BIG-IP system
http://support.f5.com/kb/en-us/solutions/public/7000/200/sol7215.html

SOL8971: Creating transparent ICMP health monitors
https://support.f5.com/kb/en-us/solutions/public/8000/900/sol8971.html

These solutions provide the following:

• Minimal monitoring.

  • You will only need to apply monitoring to a single gateway pool on the GTM and a single gateway pool on the LTM.

• You can then apply this gateway pool to all of your internal Virtual Servers.

• The GTM will mark the links as unavailable when it detects the link has become unavailable.